Optical member, and backlight unit and image display device using said optical member

ABSTRACT

Provided is an optical member, which is suppressed from causing a reduction in display quality due to wear or a flaw resulting from its vibration while maintaining the excellent characteristics of its low-refractive index layer. The optical member includes: a light guide plate having an end surface that light from a light source enters and an emitting surface from which the entered light is emitted; and a reflective plate bonded to a side of the light guide plate opposite to the emitting surface via a double-sided pressure-sensitive adhesive film. The double-sided pressure-sensitive adhesive film includes a first pressure-sensitive adhesive layer, a low-refractive index layer, and a second pressure-sensitive adhesive layer from the light guide plate side. The optical member further includes a surface-treated layer formed on a side of the reflective plate opposite to the double-sided pressure-sensitive adhesive film.

TECHNICAL FIELD

The present invention relates to an optical member, and a backlight unitand an image display apparatus each using the optical member.

BACKGROUND ART

In the lamination of a light guide plate and a peripheral optical member(e.g., a reflective plate, a diffusing plate, a prism sheet, or a lightextraction film) in an optical apparatus in which light is extractedwith the light guide plate (e.g., an image display apparatus or alighting apparatus), a technology including performing the laminationvia a low-refractive index layer has been known. It has been reportedthat according to such technology, the intermediation of thelow-refractive index layer improves light utilization efficiency ascompared to that in the case where the lamination is simply performedwith a pressure-sensitive adhesive alone. The use of the low-refractiveindex layer in the integration of such optical members has been expectedin on-vehicle applications and/or amusement applications (e.g., anarcade game machine, and playing machines, such as a pachinko machineand a slot machine). However, the integration of the optical members(e.g., a light guide plate and a reflective plate) in the on-vehicleapplications and/or the amusement applications may reduce displayquality owing to wear or a flaw between the optical members and/orbetween each of the optical members and a casing resulting fromvibration at the time of the use of such optical member.

CITATION LIST Patent Literature

-   [PTL 1] JP 10-62626 A

SUMMARY OF INVENTION Technical Problem

The present invention has been made to solve the above-mentionedconventional problem, and a primary object of the present invention isto provide an optical member, which is suppressed from causing areduction in display quality due to wear or a flaw resulting from itsvibration while maintaining the excellent characteristics of itslow-refractive index layer.

Solution to Problem

According to one embodiment of the present invention, there is providedan optical member, including: a light guide plate having an end surfacethat light from a light source enters and an emitting surface from whichthe entered light is emitted; and a reflective plate bonded to a side ofthe light guide plate opposite to the emitting surface via adouble-sided pressure-sensitive adhesive film. The double-sidedpressure-sensitive adhesive film includes a first pressure-sensitiveadhesive layer, a low-refractive index layer, and a secondpressure-sensitive adhesive layer from a light guide plate side. Theoptical member further includes a surface-treated layer formed on a sideof the reflective plate opposite to the double-sided pressure-sensitiveadhesive film.

In one embodiment, the surface-treated layer has a dynamic frictioncoefficient of 1.0 or less.

In one embodiment, the surface-treated layer is a hard coat layer havinga pencil hardness of H or more. In one embodiment, the surface-treatedlayer further includes an outermost layer containing fluorine on asurface of the hard coat layer opposite to the reflective plate.

According to another embodiment of the present invention, there isprovided a backlight unit. The backlight unit includes: theabove-mentioned optical member; and a light source, wherein the lightsource is arranged so as to face the end surface of the light guideplate.

According to still another embodiment of the present invention, there isprovided an image display apparatus. The image display apparatusincludes: the above-mentioned backlight unit; and an image display panelarranged on an emitting surface side of the light guide plate.

Advantageous Effects of Invention

According to the present invention, in the optical member in which thelight guide plate and the reflective plate are integrated with eachother via the double-sided pressure-sensitive adhesive film includingthe low-refractive index layer, the predetermined surface-treated layeris arranged on the surface of the reflective plate. Thus, there can berealized the optical member, which is suppressed from causing areduction in display quality due to wear or a flaw resulting from itsvibration while maintaining the excellent characteristics of thelow-refractive index layer.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic sectional view of an optical member according toone embodiment of the present invention.

DESCRIPTION OF EMBODIMENTS

Embodiments of the present invention are described below. However, thepresent invention is not limited to these embodiments.

A. Overall Configuration of Optical Member FIG. 1 is a schematicsectional view of an optical member according to one embodiment of thepresent invention. An optical member 100 of the illustrated exampleincludes a light guide plate 10 and a reflective plate 30 bonded to thelight guide plate 10 via a double-sided pressure-sensitive adhesive film20. The double-sided pressure-sensitive adhesive film 20 includes afirst pressure-sensitive adhesive layer 21, a low-refractive index layer22, and a second pressure-sensitive adhesive layer 23 from the lightguide plate 10 side. Practically, a substrate 24 is arranged between thelow-refractive index layer 22 and the second pressure-sensitive adhesivelayer 23. More specifically, the low-refractive index layer 22 may beformed on the surface of the substrate 24, and the firstpressure-sensitive adhesive layer 21 and the second pressure-sensitiveadhesive layer 23 may be arranged on both the sides of the laminate ofthe substrate 24 and the low-refractive index layer 22. The opticalmember 100 further includes a surface-treated layer 40 formed on theside of the reflective plate 30 opposite to the double-sidedpressure-sensitive adhesive film 20.

The light guide plate 10 has an end surface 10 a that light from a lightsource enters and an emitting surface 10 b from which the entered lightis emitted. That is, the light guide plate 10 is typically an edge lightsystem in which the light enters from the end surface 10 a. Morespecifically, the light guide plate 10 guides the light that has enteredthe end surface 10 a from the light source toward an end portionopposite to the end surface 10 a while subjecting the light to areflective action or the like therein, and in the light guide process,the plate gradually emits the light from the emitting surface 10 b. Anemission pattern is typically arranged on the emitting surface 10 b. Theemission pattern is, for example, an uneven shape. Further, a lightextraction pattern is typically arranged on the surface of the lightguide plate opposite to the emitting surface. The light extractionpattern is, for example, a white dot. Any appropriate light guide platemay be used as the light guide plate. Any appropriate material may beused as a material for forming the light guide plate as long as thelight applied from the light source can be efficiently guided. Examplesof the material for forming the light guide plate include an acrylicresin such as polymethyl methacrylate (PMMA), a polycarbonate (PC)resin, a polyethylene terephthalate (PET) resin, a styrene resin, andglass.

Any appropriate reflective plate may be used as the reflective plate.For example, the reflective plate may be a mirror-surface reflectiveplate, or may be a diffusing reflective plate. Specific examples of thereflective plate include: a resin sheet having a high reflectance (e.g.,an acrylic plate); a metal thin plate or metal foil made of aluminum,stainless steel, or the like; a deposited sheet obtained by depositingaluminum, silver, or the like from the vapor onto a substrate such as aresin film made of polyester or the like; a laminate of a substrate suchas a resin film made of polyester or the like and metal foil made ofaluminum or the like; and a resin film having formed therein voids.

The double-sided pressure-sensitive adhesive film and thesurface-treated layer for forming the optical member are described indetail below. Description for the light guide plate and the reflectiveplate except the foregoing is omitted because configurations well-knownin the art may be adopted for the plates.

B. Double-Sided Pressure-Sensitive Adhesive Film B-1. Outline ofDouble-Sided Pressure-Sensitive Adhesive Film

As described in the section A, the double-sided pressure-sensitiveadhesive film includes the first pressure-sensitive adhesive layer 21,the low-refractive index layer 22, and practically, the substrate 24,and the second pressure-sensitive adhesive layer 23 from the light guideplate 10 side. The porosity of the low-refractive index layer 22 is, forexample, 40 vol % or more. The storage modulus of elasticity of thefirst pressure-sensitive adhesive layer at 23° C. is, for example, from1.0×10⁵ (Pa) to 1.0×10⁷ (Pa), and the storage modulus of elasticity ofthe second pressure-sensitive adhesive layer at 23° C. is, for example,1.0×10⁵ (Pa) or less. When the storage modulus of elasticity of thefirst pressure-sensitive adhesive layer adjacent to the low-refractiveindex layer is set to be high as described above, the pressure-sensitiveadhesive of the layer can be prevented from entering the pores of thelow-refractive index layer. Accordingly, the refractive index of thelow-refractive index layer is maintained low, and the lowering effectcan be maintained. Further, when the storage modulus of elasticity ofthe second pressure-sensitive adhesive layer that is the otherpressure-sensitive adhesive layer is set to be low as described above,the breakage of the low-refractive index layer due to the vibration ofthe optical member can be suppressed. The suppressing effect on thebreakage of the low-refractive index layer due to the vibration becomesparticularly significant when the optical member is used in on-vehicleapplications and/or amusement applications.

In one embodiment, the ratio of the thickness of the low-refractiveindex layer to the total thickness of the pressure-sensitive adhesivelayers present in the double-sided pressure-sensitive adhesive film is,for example, from 0.10% to 5.00%, preferably from 0.11% to 4.50%, morepreferably from 0.12% to 4.00%. When the thickness ratio falls withinsuch ranges, the breakage of the low-refractive index layer due to thevibration can be more satisfactorily suppressed. More specifically,although large vibration is present not only in a longitudinal directionbut also in a lateral direction in on-vehicle applications and/oramusement applications, the breakage of the low-refractive index layerparticularly poor in strength in the lateral direction can besatisfactorily suppressed.

B-2. Substrate

The substrate may be typically formed of a film or plate-shaped productof a resin (preferably a transparent resin). Typical examples of suchresin include a thermoplastic resin and a reactive resin (e.g., anionizing radiation-curable resin). Specific examples of thethermoplastic resin include: a (meth)acrylic resin, such as polymethylmethacrylate (PMMA) or polyacrylonitrile; a polycarbonate (PC) resin; apolyester resin such as PET; a cellulose-based resin such as triacetylcellulose (TAC); a cyclic polyolefin-based resin; and a styrene-basedresin. Specific examples of the ionizing radiation-curable resin includean epoxy acrylate-based resin and a urethane acrylate-based resin. Thoseresins may be used alone or in combination thereof.

The thickness of the substrate is, for example, from 10 μm to 100 μm,preferably from 10 μm to 50 μm.

The refractive index of the substrate is preferably 1.47 or more, morepreferably from 1.47 to 1.60, still more preferably from 1.47 to 1.55.When the refractive index falls within such ranges, light extracted fromthe light guide plate can be introduced into the image display cellwithout being adversely affected.

B-3. Low-Refractive Index Layer

The low-refractive index layer typically has pores therein. The porosityof the low-refractive index layer is 40 vol % or more as describedabove, and is typically 50 vol % or more, preferably 70 vol % or more,more preferably 80 vol % or more. Meanwhile, the porosity is, forexample, 90 vol % or less, preferably 85 vol % or less. When theporosity falls within the ranges, the refractive index of thelow-refractive index layer can be set within an appropriate range. Theporosity is a value calculated from the value of the refractive indexmeasured with an ellipsometer by using Lorentz-Lorenz's formula.

The refractive index of the low-refractive index layer is preferably1.30 or less, more preferably 1.20 or less, still more preferably 1.15or less. The lower limit of the refractive index may be, for example,1.01. When the refractive index falls within such ranges, extremelyexcellent light utilization efficiency can be achieved in the laminatedstructure of the light guide plate and the peripheral member obtainedvia the optical laminate with pressure-sensitive adhesive layers on bothsides. The refractive index refers to a refractive index measured at awavelength of 550 nm unless otherwise stated. The refractive index is avalue measured by a method described in [Production Example 4] inExamples below.

Any appropriate configuration may be adopted for the low-refractiveindex layer as long as the layer has the above-mentioned desiredporosity and refractive index. The low-refractive index layer may bepreferably formed through, for example, application or printing.Materials described in, for example, WO 2004/113966 A1, JP 2013-254183A, and JP 2012-189802 A may each be adopted as a material for formingthe low-refractive index layer. Specific examples thereof include:silica-based compounds; hydrolyzable silanes, and partial hydrolysatesand dehydration condensates thereof; organic polymers; silanolgroup-containing silicon compounds; active silica obtained by bringing asilicate into contact with an acid or an ion-exchange resin;polymerizable monomers (e.g., a (meth)acrylic monomer and astyrene-based monomer); curable resins (e.g., a (meth)acrylic resin, afluorine-containing resin, and a urethane resin); and combinationsthereof. The low-refractive index layer may be formed by, for example,applying or printing a solution or a dispersion liquid of such material.

The size of each of the pores (holes) in the low-refractive index layerrefers to a major axis diameter out of the major axis diameter and minoraxis diameter of the pore (hole). The sizes of the pores (holes) are,for example, from 2 nm to 500 nm. The sizes of the pores (holes) are,for example, 2 nm or more, preferably 5 nm or more, more preferably 10nm or more, still more preferably 20 nm or more. Meanwhile, the sizes ofthe pores (holes) are, for example, 500 nm or less, preferably 200 nm orless, more preferably 100 nm or less. The range of the sizes of thepores (holes) is, for example, from 2 nm to 500 nm, preferably from 5 nmto 500 nm, more preferably from 10 nm to 200 nm, still more preferablyfrom 20 nm to 100 nm. The sizes of the pores (holes) may be adjusted todesired sizes in accordance with, for example, a purpose and anapplication.

The sizes of the pores (holes) may be quantified by a BET test method.Specifically, 0.1 g of the sample (formed pore layer) is loaded into thecapillary of a specific surface area-measuring apparatus (manufacturedby Micromeritics Instrument Corporation, ASAP 2020), and is then driedunder reduced pressure at room temperature for 24 hours so that a gas inits pore structure may be removed. Then, an adsorption isotherm is drawnby causing the sample to adsorb a nitrogen gas, and its pore sizedistribution is determined. Thus, the pore sizes may be evaluated.

The haze of the low-refractive index layer is, for example, less than5%, preferably less than 3%. Meanwhile, the haze is, for example, 0.1%or more, preferably 0.2% or more. The range of the haze is, for example,0.1% or more and less than 5%, preferably 0.2% or more and less than 3%.The haze may be measured by, for example, such a method as describedbelow. The haze is an indicator of the transparency of thelow-refractive index layer.

The pore layer (low-refractive index layer) is cut into a size measuring50 mm by 50 mm, and is set in a haze meter (manufactured by MurakamiColor Research Laboratory Co., Ltd.: HM-150), followed by themeasurement of its haze. The haze value is calculated from the followingequation.

Haze (%)=[diffuse transmittance (%)/total light transmittance(%)]×100(%)

The low-refractive index layer having the pores therein is, for example,a low-refractive index layer having a porous layer and/or an air layerin at least part thereof. The porous layer typically contains aerogeland/or particles (e.g., hollow fine particles and/or porous particles).The low-refractive index layer may be preferably a nanoporous layer(specifically a porous layer in which the diameters of 90% or more ofmicropores fall within the range of from 10⁻¹ nm to 10³ nm).

Any appropriate particles may be adopted as the particles. The particlesare each typically formed of a silica-based compound. Examples of theshapes of the particles include a spherical shape, a plate shape, aneedle shape, a string shape, and a botryoidal shape. String-shapedparticles are, for example, particles in which a plurality of particleseach having a spherical shape, a plate shape, or a needle shape arestrung together like beads, short fiber-shaped particles (e.g., shortfiber-shaped particles described in JP 2001-188104 A), and a combinationthereof. The string-shaped particles may be linear or may be branched.Botryoidal-shaped particles are, for example, particles in which aplurality of spherical, plate-shaped, and needle-shaped particlesaggregate to form a botryoidal shape. The shapes of the particles may beidentified through, for example, observation with a transmissionelectron microscope.

The thickness of the low-refractive index layer is preferably from 0.2μm to 5 μm, more preferably from 0.3 μm to 3 μm. When the thickness ofthe low-refractive index layer falls within such ranges, adamage-preventing effect exhibited by the present invention becomessignificant. Further, the above-mentioned desired thickness ratio can beeasily achieved.

As described above, the low-refractive index layer may be typicallyformed through application or printing. With such configuration, thelow-refractive index layer can be continuously arranged by aroll-to-roll process. The low-refractive index layer may be formed onthe entire surface of the substrate, or may be formed in a predeterminedpattern. When the low-refractive index layer is formed in thepredetermined pattern, the application is performed through, forexample, a mask having the predetermined pattern. Any appropriate systemmay be adopted for the printing. Specifically, a printing method may bea plate printing method, such as gravure printing, offset printing, orflexographic printing, or may be a plateless printing method, such asinkjet printing, laser printing, or electrostatic printing.

An example of a specific configuration of the low-refractive index layeris described below. The low-refractive index layer of this embodiment isformed of one or a plurality of kinds of constituent units each forminga fine pore structure, and the constituent units are chemically bondedto each other through a catalytic action. Examples of the shape of eachof the constituent units include a particle shape, a fiber shape, a rodshape, and a flat plate shape. The constituent units may have only oneshape, or may have two or more shapes in combination. In the followingdescription, a case in which the low-refractive index layer is a porelayer of a porous body in which the microporous particles are chemicallybonded to each other is mainly described.

Such pore layer may be formed by, for example, chemically bonding themicroporous particles to each other in a pore layer-forming step. In theembodiment of the present invention, the shapes of the “particles”(e.g., the microporous particles) are not particularly limited. Forexample, the shapes may each be a spherical shape, or may each be anyother shape. In addition, in the embodiment of the present invention,the microporous particles may be, for example, sol-gel beaded particles,nanoparticles (hollow nanosilica nanoballoon particles), or nanofibers.The microporous particles each typically contain an inorganic substance.Specific examples of the inorganic substance include silicon (Si),magnesium (Mg), aluminum (Al), titanium (Ti), zinc (Zn), and zirconium(Zr). Those inorganic substances may be used alone or in combinationthereof. In one embodiment, the microporous particles are, for example,microporous particles of a silicon compound, and the porous body is, forexample, a silicone porous body. The microporous particles of thesilicon compound each contain, for example, a pulverized body of agel-like silica compound. In addition, another form of thelow-refractive index layer having the porous layer and/or the air layerin at least part thereof is, for example, a pore layer having thefollowing features: the layer is formed of fibrous substances such asnanofibers; and the fibrous substances are entangled with each other toform pores, thereby forming the layer. A method of producing such porelayer is not particularly limited, and is the same as that in the caseof, for example, the pore layer of the porous body in which themicroporous particles are chemically bonded to each other. Still anotherform thereof is, for example, a pore layer using hollow nanoparticles ornanoclay, or a pore layer formed by using hollow nanoballoons ormagnesium fluoride. The pore layer may be a pore layer formed of asingle constituent substance, or may be a pore layer formed of aplurality of constituent substances. The pore layer may include any oneof the above-mentioned forms, or may include two or more of theabove-mentioned forms.

In this embodiment, the porous structure of the porous body may be, forexample, an open-cell structural body in which hole structures arecontinuous with each other. The open-cell structural body means, forexample, that the hole structures are three-dimensionally continuouswith each other in the silicone porous body, and can be said to be astate in which the internal pores of the hole structures are continuouswith each other. When the porous body has an open-cell structure, itsporosity can be increased. However, when closed-cell particles(particles each individually having a hole structure) such as hollowsilica are used, an open-cell structure cannot be formed. Meanwhile, forexample, when silica sol particles (pulverized products of a gel-likesilicon compound that forms sol) are used, the particles each have athree-dimensional dendritic structure, and hence the dendritic particlesare sedimented and deposited in a coating film (coating film of the solcontaining the pulverized products of the gel-like silicon compound).Accordingly, an open-cell structure can be easily formed. Thelow-refractive index layer more preferably has a monolith structure inwhich an open-cell structure includes a plurality of pore sizedistributions. The monolith structure means, for example, a hierarchicalstructure including a structure in which nanosized fine pores arepresent and an open-cell structure in which the nanosized poresassemble. When the monolith structure is formed, both of film strengthand a high porosity may be achieved by, for example, imparting the highporosity to the layer through use of a coarse open-cell pore whileimparting the film strength thereto through use of a fine pore. Suchmonolith structure may be preferably formed by controlling the pore sizedistribution of a pore structure to be produced in the gel (gel-likesilicon compound) at a stage before its pulverization into the silicasol particles. In addition, the monolith structure may be formed by, forexample, controlling the particle size distribution of the silica solparticles after the pulverization to a desired size at the time of thepulverization of the gel-like silicon compound.

The low-refractive index layer contains, for example, the pulverizedproducts of a gel-like compound as described above, and the pulverizedproducts are chemically bonded to each other. The form of the chemicalbond (chemical bonding) between the pulverized products in thelow-refractive index layer is not particularly limited, and examplesthereof include a cross-linking bond, a covalent bond, and a hydrogenbond.

The gel form of the gel-like compound is not particularly limited. Theterm “gel” generally refers to a state in which the mixture of a solventand a solute is solidified because the solute loses its independentmobility owing to an interaction between its molecules to have astructure in which the molecules assemble. For example, the gel-likecompound may be wet gel or xerogel. In general, the wet gel refers togel which contains a dispersion medium and in which a solute has auniform structure in the dispersion medium, and the xerogel refers togel from which a solvent is removed, and in which a solute has a networkstructure having pores.

The gel-like compound is, for example, a gelled product obtained bycausing a monomer compound to gel. The gel-like silicon compound isspecifically, for example, a gelled product in which the molecules of amonomer silicon compound are bonded to each other, and the gelledproduct is more specifically, for example, a gelled product in which themolecules of the monomer silicon compound are bonded to each other by acovalent bond, a hydrogen bond, or an intermolecular force. The covalentbond is, for example, a bond formed by dehydration condensation.

The volume-average particle diameter of the pulverized products in thelow-refractive index layer is, for example, 0.10 μm or more, preferably0.20 μm or more, more preferably 0.40 μm or more. Meanwhile, thevolume-average particle diameter is, for example, 2.00 μm or less,preferably 1.50 μm or less, more preferably 1.00 μm or less. The rangeof the volume-average particle diameter is, for example, from 0.10 μm to2.00 μm, preferably from 0.20 μm to 1.50 μm, more preferably from 0.40μm to 1.00 μm. The particle size distribution of the pulverized productsmay be measured with, for example, a particle sizedistribution-evaluating apparatus based on a dynamic light scatteringmethod, a laser diffraction method, or the like, and an electronmicroscope, such as a scanning electron microscope (SEM) or atransmission electron microscope (TEM). The volume-average particlediameter is an indicator of a variation in particle size of thepulverized products.

The kind of the gel-like compound is not particularly limited. Thegel-like compound is, for example, a gel-like silicon compound. Althoughdescription is given below by taking a case in which the gel-likecompound is the gel-like silicon compound as an example, the gel-likecompound is not limited thereto.

The above-mentioned cross-linking bond is, for example, a siloxane bond.Examples of the siloxane bond include such a bond T2, a bond T3, and abond T4 as represented below. When the pore layer (low-refractive indexlayer) has a siloxane bond, the layer may have any one kind of thosebonds, may have any two kinds of the bonds, or may have all the threekinds of the bonds. As the ratios of the T2 and the T3 out of thesiloxane bonds become larger, the layer becomes richer in flexibility,and hence characteristics intrinsic to gel can be expected. Meanwhile,as the ratio of the T4 becomes larger, the film strength of the layer ismore easily expressed. Accordingly, the ratios of the T2, the T3, andthe T4 are preferably changed in accordance with, for example, purposes,applications, and desired characteristics.

In addition, in the low-refractive index layer (pore layer), forexample, silicon atoms to be incorporated preferably form a siloxanebond. As a specific example, the ratio of unbonded silicon atoms (inother words, residual silanol groups) out of all the silicon atoms inthe pore layer is, for example, less than 50%, preferably 30% or less,more preferably 15% or less.

When the gel-like compound is a gel-like silicon compound, a monomersilicon compound is not particularly limited. The monomer siliconcompound is, for example, a compound represented by the below-indicatedformula (1). When the gel-like silicon compound is a gelled product inwhich the molecules of the monomer silicon compound are bonded to eachother by a hydrogen bond or an intermolecular force as described above,a hydrogen bond may be formed between the molecules of the monomerrepresented by the formula (1) through, for example, their respectivehydroxy groups.

In the formula (1), X represents, for example, 2, 3, or 4, preferably 3or 4. R=represents, for example, a linear or branched alkyl group. Thegroup represented by R¹ has, for example, 1 to 6 carbon atoms,preferably 1 to 4 carbon atoms, more preferably 1 or 2 carbon atoms.Examples of the linear alkyl group include a methyl group, an ethylgroup, a propyl group, a butyl group, a pentyl group, and a hexyl group,and examples of the branched alkyl group include an isopropyl group andan isobutyl group.

A specific example of the silicon compound represented by the formula(1) is a compound represented by the below-indicated formula (1′) inwhich X represents 3. In the below-indicated formula (1′), R¹ isidentical to that in the case of the formula (1), and represents, forexample, a methyl group. When R=represents a methyl group, the siliconcompound is tris(hydroxy)methylsilane. When X represents 3, the siliconcompound is, for example, a trifunctional silane having 3 functionalgroups.

Another specific example of the silicon compound represented by theformula (1) is a compound in which X represents 4. In this case, thesilicon compound is, for example, a tetrafunctional silane having 4functional groups.

The monomer silicon compound may be, for example, a hydrolysate of asilicon compound precursor. The silicon compound precursor only needs tobe capable of producing a silicon compound through, for example,hydrolysis, and is specifically, for example, a compound represented bythe below-indicated formula (2).

In the formula (2), X represents, for example, 2, 3, or 4,

R¹ and R² each independently represent a linear or branched alkyl group,

R¹ and R² may be identical to or different from each other,

when X represents 2, R¹s may be identical to or different from eachother, and

R²s may be identical to or different from each other.

X and R¹ are identical to, for example, X and R¹ in the formula (1). Forexample, examples of R¹ in the formula (1) may be cited for R².

The silicon compound precursor represented by the formula (2) isspecifically, for example, a compound represented by the below-indicatedformula (2′) in which X represents 3. In the below-indicated formula(2′), R¹ and R² are each identical to that in the case of the formula(2). When R¹ and R² represent methyl groups, the silicon compoundprecursor is trimethoxy(methyl)silane (hereinafter sometimes referred toas “MTMS”).

The monomer silicon compound is preferably a trifunctional silanebecause the silane is excellent in, for example, low-refractive indexproperty. In addition, the monomer silicon compound is preferably atetrafunctional silane because the silane is excellent in, for example,strength (e.g., scratch resistance). The monomer silicon compounds maybe used alone or in combination thereof. For example, as the monomersilicon compound, only the trifunctional silane may be incorporated intothe low-refractive index layer, only the tetrafunctional silane may beincorporated, both of the trifunctional silane and the tetrafunctionalsilane may be incorporated, or any other silicon compound may be furtherincorporated. When two or more kinds of silicon compounds are used asthe monomer silicon compounds, a ratio therebetween is not particularlylimited, and may be appropriately set.

An example of a method of forming such low-refractive index layer isdescribed below.

The method typically includes: a precursor-forming step of forming apore structure, which is a precursor of the low-refractive index layer(pore layer), on a resin film; and a cross-linking reaction step ofcausing a cross-linking reaction in the precursor after theprecursor-forming step. The method further includes: a containingliquid-producing step of producing a containing liquid containingmicroporous particles (hereinafter sometimes referred to as “microporousparticle-containing liquid” or simply “containing liquid”); and a dryingstep of drying the containing liquid. In the precursor-forming step, themicroporous particles in a dried body are chemically bonded to eachother to form the precursor. The containing liquid is not particularlylimited, and is, for example, a suspension containing the microporousparticles. In the following, a case in which the microporous particlesare pulverized products of the gel-like compound, and the pore layer isa porous body (preferably a silicone porous body) containing thepulverized products of the gel-like compound is mainly described.However, even when the microporous particles are products except thepulverized products of the gel-like compound, the low-refractive indexlayer may be similarly formed.

According to the above-mentioned method, for example, a low-refractiveindex layer (pore layer) having an extremely low refractive index isformed. A reason for the foregoing is assumed to be, for example, asdescribed below. However, the assumption does not limit the method offorming the low-refractive index layer.

The above-mentioned pulverized products are obtained by pulverizing thegel-like silicon compound, and hence a state in which thethree-dimensional structure of the gel-like silicon compound before thepulverization is dispersed in a three-dimensional basic structure isestablished. Further, in the above-mentioned method, the application ofthe crushed products of the gel-like silicon compound onto the resinfilm results in the formation of the precursor of a porous structurebased on the three-dimensional basic structure. In other words,according to the method, a new porous structure (three-dimensional basicstructure) different from the three-dimensional structure of thegel-like silicon compound is formed by the application of the pulverizedproducts. Accordingly, in the pore layer to be finally obtained, such alow refractive index that the layer functions to the same extent as, forexample, an air layer does may be achieved. Further, in the method, thethree-dimensional basic structure is fixed because the pulverizedproducts are chemically bonded to each other. Accordingly, the porelayer to be finally obtained can maintain sufficient strength andsufficient flexibility despite the fact that the layer is a structurehaving pores.

Further, in the above-mentioned method, the above-mentionedprecursor-forming step and the above-mentioned cross-linking reactionstep are performed as separate steps. In addition, the cross-linkingreaction step is preferably performed in a plurality of stages. In thecase where the cross-linking reaction step is performed in a pluralityof stages, for example, the strength of the precursor is furtherimproved as compared to that in the case where the cross-linkingreaction step is performed in one stage, and hence a low-refractiveindex layer achieving both of a high porosity and high strength can beobtained. Although a mechanism for the foregoing is unclear, themechanism is assumed to be, for example, as described below. That is, asdescribed above, an improvement in film strength with a catalyst or thelike simultaneous with the formation of the pore layer involves aproblem in that the porosity of the layer reduces, though the filmstrength thereof is improved by the advancement of a catalytic reaction.This is probably because the number of cross-links (chemical bonds)between the microporous particles is increased by, for example, theadvancement of a cross-linking reaction between the microporousparticles by the catalyst, and hence the bonds therebetween becomestronger, but the entirety of the pore layer condenses to reduce theporosity. In contrast, when the precursor-forming step and thecross-linking reaction step are performed as separate steps, and thecross-linking reaction step is performed in a plurality of stages, it isassumed that the number of the cross-links (chemical bonds) can beincreased while, for example, the form of the entirety of the precursoris not changed to a very large extent (e.g., the condensation of theentirety is not caused to a very large extent). However, such mechanismis an example of assumable mechanisms, and does not limit the method offorming the low-refractive index layer.

In the precursor-forming step, for example, particles having a uniformshape are laminated to form the precursor of the pore layer. Thestrength of the precursor at the time point is extremely weak. Afterthat, a product that can chemically bond the microporous particles toeach other through, for example, a photoactive or thermally activecatalytic reaction (e.g., a strongly basic catalyst generated from aphotobase generator) is generated (first stage of the cross-linkingreaction step). When heat aging (second stage of the cross-linkingreaction step) is further performed in order that the reaction may beadvanced efficiently and in a short time period, the chemical bonding(cross-linking reaction) between the microporous particles may befurther advanced to improve the strength. For example, when themicroporous particles are microporous particles of a silicon compound(e.g., pulverized bodies of a gel-like silica compound), and residualsilanol groups (Si—OH groups) are present in the precursor, the residualsilanol groups may be chemically bonded to each other by thecross-linking reaction. However, the description is also an example, anddoes not limit the method of forming the low-refractive index layer.

The above-mentioned method includes the containing liquid-producing stepof producing the containing liquid containing the microporous particles.When the microporous particles are the pulverized products of thegel-like compound, the pulverized products are obtained by, for example,pulverizing the gel-like compound. As described above, thethree-dimensional structure of the gel-like compound is broken by thepulverization of the gel-like compound to be dispersed in thethree-dimensional basic structure. An example of the preparation of thepulverized products is as described below.

The gelation of a monomer compound may be performed by, for example,bonding the molecules of the monomer compound to each other by ahydrogen bond or an intermolecular force. The monomer compound is, forexample, a silicon compound represented by the formula (1). The siliconcompound represented by the formula (1) has hydroxy groups, and hencethe molecules of the monomer represented by the formula (1) may bebonded to each other by a hydrogen bond or an intermolecular forcethrough, for example, their respective hydroxy groups.

Alternatively, the silicon compound may be a hydrolysate of theabove-mentioned silicon compound precursor, and may be produced by, forexample, hydrolyzing the silicon compound precursor represented by theformula (2).

A method for the hydrolysis of a monomer compound precursor is notparticularly limited, and the hydrolysis may be performed by, forexample, a chemical reaction in the presence of a catalyst. Examples ofthe catalyst include acids, such as oxalic acid and acetic acid. Thehydrolysis reaction may be performed by, for example, slowly droppingand mixing an aqueous solution of oxalic acid into a mixed liquid (e.g.,a suspension) of the silicon compound precursor and dimethyl sulfoxideunder a room-temperature environment, and then stirring the mixture asit is for about 30 minutes. At the time of the hydrolysis of the siliconcompound precursor, heating and fixation after the gelation, aging, andthe formation of the pore structure subsequent to the hydrolysis may bemore efficiently performed by, for example, completely hydrolyzing thealkoxy groups of the silicon compound precursor.

The gelation of the monomer compound may be performed by, for example, adehydration condensation reaction between the molecules of the monomer.For example, the dehydration condensation reaction is preferablyperformed under the presence of a catalyst, and examples of the catalystinclude dehydration condensation catalysts including: acid catalysts,such as hydrochloric acid, oxalic acid, and sulfuric acid; and basiccatalysts, such as ammonia, potassium hydroxide, sodium hydroxide, andammonium hydroxide. A basic catalyst is preferred as the dehydrationcondensation catalyst. In the dehydration condensation reaction, theamount of the catalyst to be added to the monomer compound is notparticularly limited. The catalyst may be added in an amount of, forexample, preferably from 0.1 mol to 10 mol, more preferably from 0.05mol to 7 mol, still more preferably from 0.1 mol to 5 mol with respectto 1 mol of the monomer compound.

For example, the gelation of the monomer compound is preferablyperformed in a solvent. The ratio of the monomer compound to the solventis not particularly limited. Examples of the solvent include dimethylsulfoxide (DMSO), N-methylpyrrolidone (NMP), N,N-dimethylacetamide(DMAc), dimethylformamide (DMF), γ-butylolactone (GBL), acetonitrile(MeCN), and ethylene glycol ethyl ether (EGEE). Those solvents may beused alone or in combination thereof. The solvent to be used for thegelation is hereinafter sometimes referred to as “solvent for gelation.”

Conditions for the gelation are not particularly limited. Thetemperature at which the solvent containing the monomer compound istreated is, for example, from 20° C. to 30° C., preferably from 22° C.to 28° C., more preferably from 24° C. to 26° C. A treatment time is,for example, from 1 minute to 60 minutes, preferably from 5 minutes to40 minutes, more preferably from 10 minutes to 30 minutes. When thedehydration condensation reaction is performed, treatment conditionstherefor are not particularly limited, and those examples may be cited.When the gelation is performed, for example, a siloxane bond grows toform silica primary particles. As the reaction further advances, theprimary particles are strung together like beads to produce gel having athree-dimensional structure.

The gel-like compound obtained by the gelation is preferably subjectedto aging treatment after the gelation reaction. The aging treatment mayfurther grow, for example, the primary particles of the gel having athree-dimensional structure, which has been obtained by the gelation, toincrease the sizes of the particles themselves. As a result, the contactstate of a neck portion where the particles are brought into contactwith each other can be changed from point contact to surface contact(the area of the contact therebetween can be increased). In the gelsubjected to the aging treatment, for example, the strength of the gelitself is improved, and as a result, the strength of thethree-dimensional basic structure after the performance of thepulverization of the gel can be improved. Thus, in, for example, thedrying step after the application of the pulverized products, the poresize of the pore structure having deposited thereon thethree-dimensional basic structure can be suppressed from shrinking alongwith the volatilization of the solvent in the drying process.

The aging treatment may be performed by, for example, incubating thegel-like compound at a predetermined temperature for a predeterminedtime period. An aging temperature is, for example, 30° C. or more,preferably 35° C. or more, more preferably 40° C. or more. Meanwhile,the aging temperature is, for example, 80° C. or less, preferably 75° C.or less, more preferably 70° C. or less. The range of the agingtemperature is, for example, from 30° C. to 80° C., preferably from 35°C. to 75° C., more preferably from 40° C. to 70° C. An aging time is,for example, 5 hours or more, preferably 10 hours or more, morepreferably 15 hours or more. Meanwhile, the aging time is, for example,50 hours or less, preferably 40 hours or less, more preferably 30 hoursor less. The range of the aging time is, for example, from 5 hours to 50hours, preferably from 10 hours to 40 hours, more preferably from 15hours to 30 hours. The aging conditions may be optimized so that, forexample, an increase in size of each of the silica primary particles andan increase in contact area of the neck portion may be achieved.Further, the boiling point of a solvent to be used is preferably takeninto consideration. For example, when the aging temperature isexcessively high, the solvent may excessively volatilize to cause aninconvenience such as the closing of the pores of a three-dimensionalpore structure due to the condensation of the concentration of a coatingliquid (gel liquid). Meanwhile, for example, when the aging temperatureis excessively low, an effect exhibited by the aging is not sufficientlyobtained, and moreover, the temperature variation of a mass productionprocess for the low-refractive index layer with time increases.Accordingly, a low-refractive index layer poor in characteristics may beformed.

For example, the same solvent as that in the gelation treatment may beused in the aging treatment. Specifically, a reaction product after thegelation treatment (in other words, the solvent containing the gel-likecompound) is preferably subjected as it is to the aging treatment. Thenumber of moles of residual silanol groups in the gel (the gel-likecompound such as a gel-like silicon compound) that has finished beingsubjected to the aging treatment after the gelation is, for example, 50%or less, preferably 40% or less, more preferably 30% or less. Meanwhile,the number of moles of the residual silanol groups is, for example, 1%or more, preferably 3% or more, more preferably 5% or more. The range ofthe number of moles of the residual silanol groups is, for example, from1% to 50%, preferably from 3% to 40%, more preferably from 5% to 30%.For the purpose of improving the hardness of the gel, for example, thenumber of moles of the residual silanol groups is preferably as low aspossible. When the number of moles of the silanol groups is excessivelyhigh, for example, there is a risk in that the pore structure cannot beretained until the precursor of the silicone porous body iscross-linked. Meanwhile, when the number of moles of the silanol groupsis excessively low, for example, there is a risk in that the pulverizedproducts of the gel-like compound cannot be cross-linked in the step ofproducing the microporous particle-containing liquid (e.g., asuspension) and/or any subsequent step, and hence sufficient filmstrength cannot be imparted to the low-refractive index layer. Thenumber of moles of the residual silanol groups is, for example, theratio of the residual silanol groups when the number of moles of thealkoxy groups of a raw material (e.g., the monomer compound precursor)is defined as 100. Although the foregoing example concerns a silanolgroup, for example, when the monomer silicon compound is modified withvarious reactive functional groups, the same matters, conditions, andthe like may be applied to each of the functional groups.

After the monomer compound has been gelled in the solvent for gelation,the resultant gel-like compound is pulverized. In the pulverization, forexample, the gel-like compound in the solvent for gelation may besubjected as it is to pulverization treatment. Alternatively, thefollowing may be performed: the solvent for gelation is replaced withany other solvent; and then the gel-like compound in the other solventis subjected to the pulverization treatment. In addition, for example,when a catalyst used in the gelation reaction and the used solventremain even after the aging step to cause the gelation of a liquidobtained through the step with time (pot life) and a reduction in dryingefficiency at the time of the drying step, the solvent is preferablyreplaced with the other solvent. The other solvent is hereinaftersometimes referred to as “solvent for pulverization.”

The solvent for pulverization is not particularly limited, and forexample, an organic solvent may be used. The organic solvent is, forexample, a solvent having a boiling point of, for example, 130° C. orless, preferably 100° C. or less, more preferably 85° C. or less.Specific examples thereof include isopropyl alcohol (IPA), ethanol,methanol, butanol, propylene glycol monomethyl ether (PGME), methylcellosolve, acetone, dimethylformamide (DMF), and isobutyl alcohol.Those solvents for pulverization may be used alone or in combinationthereof.

The combination of the solvent for gelation and the solvent forpulverization is not particularly limited, and examples thereof includecombinations of DMSO and IPA, of DMSO and ethanol, of DMSO and methanol,of DMSO and butanol, and of DMSO and isobutyl alcohol. When the solventfor gelation is replaced with the solvent for crushing as describedabove, a more uniform coating film may be formed in, for example,coating film formation to be described later.

A method of pulverizing the gel-like compound is not particularlylimited, and the pulverization may be performed with, for example, anultrasonic homogenizer, a high-speed rotary homogenizer, or any otherpulverization apparatus using a cavitation phenomenon. While anapparatus for performing media pulverization such as a ball millphysically breaks the pore structure of the gel at the time of, forexample, the pulverization, a pulverization apparatus of a cavitationsystem such as a homogenizer is, for example, a media-less system, andhence peels a bonded surface between silica particles bonded to eachother in a relatively weak manner, which have already been included in agel three-dimensional structure, with a high-speed shear force. Thus,the gel three-dimensional structure to be obtained may retain, forexample, a pore structure having a particle size distribution in acertain range, and hence enables the re-formation of a pore structure bythe deposition of the pulverized products at the time of theirapplication and drying. Conditions for the pulverization are notparticularly limited, and it is preferred that the gel can be pulverizedwithout the volatilization of the solvent by, for example, momentarilyapplying a high-speed flow to the pulverized products. For example, thepulverization is preferably performed so that pulverized products havingsuch particle size variation (e.g., a volume-average particle diameteror a particle size distribution) as described above may be obtained. Ifa workload, such as a pulverization time or strength, is insufficient,there is, for example, a risk in that coarse particles remain in thelow-refractive index layer to preclude the formation of dense pores, andmoreover, the number of the appearance defects of the layer increases tomake it impossible to obtain high quality. Meanwhile, when the workloadis excessively large, there is, for example, a risk in that particleshaving a particle size distribution finer than a desired one areobtained, and hence the pore size of the pore structure deposited afterthe application and the drying becomes finer to make it impossible toobtain a desired porosity.

Thus, the liquid (e.g., a suspension) containing the microporousparticles (pulverized products of the gel-like compound) may beproduced. Further, when a catalyst that chemically bonds the microporousparticles to each other is added after the production of the liquidcontaining the microporous particles or during the production step, acontaining liquid containing the microporous particles and the catalystmay be produced. The catalyst may be, for example, a catalyst thataccelerates cross-linking bonding between the microporous particles. Adehydration condensation reaction between residual silanol groups insilica sol molecules is preferably utilized as a chemical reaction thatchemically bonds the microporous particles to each other. Theacceleration of the reaction between the hydroxy groups of the silanolgroups with the catalyst enables continuous film formation in which thepore structure is cured in a short time period. Examples of the catalystinclude a photoactive catalyst and a thermally active catalyst.According to the photoactive catalyst, in, for example, theprecursor-forming step, the microporous particles can be chemicallybonded (e.g., cross-linking bonded) to each other without heating. Inthis case, in, for example, the precursor-forming step, the shrinkage ofthe entirety of the precursor hardly occurs, and hence a higher porositycan be maintained. In addition, a substance that generates a catalyst(catalyst generator) may be used in addition to, or instead of, thecatalyst. For example, a substance that generates a catalyst with light(photocatalyst generator) may be used in addition to, or instead of, thephotoactive catalyst, and a substance that generates a catalyst withheat (thermal catalyst generator) may be used in addition to, or insteadof, the thermally active catalyst. Examples of the photocatalystgenerator include a photobase generator (substance that generates abasic catalyst when irradiated with light) and a photoacid generator(substance that generates an acid catalyst when irradiated with light).Of those, a photobase generator is preferred. Examples of the photobasegenerator include: 9-anthrylmethyl N,N-diethylcarbamate (product name:WPBG-018), (E)-1-[3-(2-hydroxyphenyl)-2-propenoyl]piperidine (productname: WPBG-027), 1-(anthraquinon-2-yl)ethyl imidazolecarboxylate(product name: WPBG-140), 2-nitrophenylmethyl4-methacryloyloxypiperidine-1-carboxylate (product name: WPBG-165),1,2-diisopropyl-3-[bis(dimethylamino)methylene]guanidium2-(3-benzoylphenyl)propionate (product name: WPBG-266), and1,2-dicyclohexyl-4,4,5,5-tetramethylbiguanidium n-butyltriphenylborate(product name: WPBG-300); 2-(9-oxoxanthen-2-yl)propionic acid1,5,7-triazabicyclo[4.4.0]dec-5-ene (manufactured by Tokyo ChemicalIndustry Co., Ltd.); and a compound containing 4-piperidine methanol(product name: HDPD-PB100, manufactured by Heraeus). The product namesincluding “WPBG” are product names of Wako Pure Chemical Industries,Ltd. Examples of the photoacid generator include an aromatic sulfoniumsalt (product name: SP-170, manufactured by ADEKA Corporation), atriaryl sulfonium salt (product name: CPI101A, manufactured by San-AproLtd.), and an aromatic iodonium salt (product name: Irgacure 250,manufactured by Ciba Japan K. K.). In addition, the catalyst thatchemically bonds the microporous particles to each other is not limitedto the photoactive catalyst and the photocatalyst generator, and may be,for example, a thermally active catalyst or a thermal catalyst generatorsuch as urea. Examples of the catalyst that chemically bonds themicroporous particles to each other include: basic catalysts, such aspotassium hydroxide, sodium hydroxide, and ammonium hydroxide; and acidcatalysts, such as hydrochloric acid, acetic acid, and oxalic acid. Ofthose, basic catalysts are preferred. The catalyst that chemically bondsthe microporous particles to each other or the catalyst generator may beused, for example, as follows: the catalyst or the catalyst generator isadded to a sol particle liquid (e.g., a suspension) containing thepulverized products (microporous particles) immediately before itsapplication, and the resultant mixture is used; or the catalyst or thecatalyst generator is mixed into a solvent, and the resultant mixedliquid is used. The mixed liquid may be, for example, a coating liquidobtained by directly adding and dissolving the catalyst or the catalystgenerator in the sol particle liquid, a solution obtained by dissolvingthe catalyst or the catalyst generator in the solvent, or a dispersionliquid obtained by dispersing the catalyst or the catalyst generator inthe solvent. The solvent is not particularly limited, and examplesthereof include water and a buffer solution.

In addition, for example, a cross-linking aid for indirectly bonding thepulverized products of the gel to each other may be further added to thegel-containing liquid. When the cross-linking aid enters a gap betweenthe particles (the pulverized products), and hence the particles and thecross-linking aid interact with, or are bonded to, each other, even theparticles distant from each other by some distance can be bonded to eachother, and hence the strength of the precursor can be efficientlyimproved. The cross-linking aid is preferably a multi-cross-linkedsilane monomer. Specifically, the multi-cross-linked silane monomer has,for example, 2 or more and 3 or less alkoxysilyl groups, may have achain length of 1 or more and 10 or less carbon atoms between thealkoxysilyl groups, and may contain an element other than carbon.Examples of the cross-linking aid include bis(trimethoxysilyl)ethane,bis(triethoxysilyl)ethane, bis(trimethoxysilyl)methane,bis(triethoxysilyl)methane, bis(triethoxysilyl)propane,bis(trimethoxysilyl)propane, bis(triethoxysilyl)butane,bis(trimethoxysilyl)butane, bis(triethoxysilyl)pentane,bis(trimethoxysilyl)pentane, bis(triethoxysilyl) hexane,bis(trimethoxysilyl) hexane,bis(trimethoxysilyl)-N-butyl-N-propyl-ethane-1,2-diamine,tris-(3-trimethoxysilylpropyl) isocyanurate, andtris-(3-triethoxysilylpropyl) isocyanurate. The addition amount of thecross-linking aid is not particularly limited, but is, for example, from0.01 wt % to 20 wt %, from 0.05 wt % to 15 wt %, or from 0.1 wt % to 10wt % with respect to the weight of the pulverized products of thesilicon compound.

Next, the containing liquid (e.g., a suspension) containing themicroporous particles is applied onto the substrate (applying step). Forexample, various application systems to be described later may each beused in the application, and a system for the application is not limitedthereto. Direct application of the containing liquid containing themicroporous particles (e.g., the pulverized products of the gel-likesilica compound) onto the substrate may form a coating film containingthe microporous particles and the catalyst. The coating film may bereferred to as, for example, “coating layer”. When the coating film isformed, for example, the pulverized products whose three-dimensionalstructures have been broken are sedimented and deposited to build a newthree-dimensional structure. For example, the containing liquidcontaining the microporous particles may be free of the catalyst thatchemically bonds the microporous particles to each other. For example,as described later, the precursor-forming step may be performed afterthe catalyst that chemically bonds the microporous particles to eachother has been blown onto the coating film, or while the catalyst isblown onto the film. However, the containing liquid containing themicroporous particles may contain the catalyst that chemically bonds themicroporous particles to each other, and the microporous particles maybe chemically bonded to each other through the action of the catalyst inthe coating film to form the precursor of the porous body.

The above-mentioned solvent (hereinafter sometimes referred to as“solvent for application”) is not particularly limited, and for example,an organic solvent may be used. An example of the organic solvent is asolvent having a boiling point of 150° C. or less. Specific examplesthereof include IPA, ethanol, methanol, n-butanol, 2-butanol, isobutylalcohol, and pentanol. In addition, the same solvent as the solvent forpulverization may be used. When the method of forming the low-refractiveindex layer includes the step of pulverizing the gel-like compound, inthe step of forming the coating film, for example, the solvent forpulverization containing the pulverized products of the gel-likecompound may be used as it is.

In the applying step, it is preferred that, for example, sol-likepulverized products dispersed in the solvent (hereinafter sometimesreferred to as “sol particle liquid”) be applied onto the substrate.When the sol particle liquid is subjected to the chemical cross-linkingafter having been, for example, applied onto the substrate and dried, apore layer having a certain level or more of film strength can becontinuously formed. The term “sol” as used in the embodiment of thepresent invention refers to the following state: when thethree-dimensional structure of the gel is pulverized, silica solparticles each having a nano three-dimensional structure retaining partof the pore structure are dispersed in the solvent to show fluidity.

The concentration of the pulverized products in the solvent forapplication is not particularly limited, and is, for example, from 0.3%(v/v) to 50% (v/v), preferably from 0.5% (v/v) to 30% (v/v), morepreferably from 1.0% (v/v) to 10% (v/v). When the concentration of thepulverized products is excessively high, for example, the fluidity ofthe sol particle liquid may remarkably reduce to cause an aggregate oran application stripe at the time of its application. When theconcentration of the pulverized products is excessively low, there is,for example, a risk in that the drying of the solvent of the solparticle liquid takes a considerable time period, and moreover, theamount of the residual solvent immediately after the drying increases toreduce the porosity of the pore layer.

The physical properties of the sol are not particularly limited. Theshear viscosity of the sol is, for example, 100 cPa·s or less,preferably 10 cPa·s or less, more preferably 1 cPa·s or less at a shearrate of 10,001 s⁻¹. When the shear viscosity is excessively high, forexample, an application stripe may occur to cause an inconvenience suchas a reduction in transfer ratio of gravure coating. In contrast, whenthe shear viscosity is excessively low, there is, for example, a risk inthat the wet coating thickness of the sol at the time of its applicationcannot be made thick, and hence a desired thickness is not obtainedafter its drying.

The amount of the pulverized products to be applied to the substrate isnot particularly limited, and may be appropriately set in accordancewith, for example, a desired thickness of the silicone porous body(consequently, the low-refractive index layer). As a specific example,when a silicone porous body having a thickness of from 0.1 μm to 1,000μm is formed, the amount of the pulverized products to be applied to thesubstrate is, for example, from 0.01 μg to 60,000 μg, preferably from0.1 μg to 5,000 μg, more preferably from 1 μg to 50 μg per 1 m² of thearea of the substrate. It is difficult to uniquely define a preferredapplication amount of the sol particle liquid because the amount isrelated to, for example, the concentration and application system of theliquid. However, the liquid is preferably applied so as to be as thin alayer as possible in consideration of productivity. When the applicationamount is excessively large, for example, the liquid is more likely tobe dried in a drying furnace before its solvent volatilizes. Thus,before the nano-pulverized sol particles are sedimented and deposited inthe solvent to form the pore structure, the solvent may be dried toinhibit the formation of the pores, thereby largely reducing theporosity of the low-refractive index layer. Meanwhile, when theapplication amount is excessively small, the following risk may behigher: application repelling occurs owing to, for example, theunevenness of the substrate, or a variation in hydrophilicity orhydrophobicity thereof.

Further, the method of forming the low-refractive index layer includes,for example, the precursor-forming step of forming the pore structurethat is the precursor of the pore layer (low-refractive index layer) onthe substrate as described above. Although the precursor-forming step isnot particularly limited, the precursor (pore structure) may be formedby, for example, the drying step of drying a coating film produced byapplying the microporous particle-containing liquid. Through dryingtreatment in the drying step, for example, the solvent in the coatingfilm (solvent in the sol particle liquid) is removed. In addition, thesol particles can be sedimented and deposited to form the pore structureduring the drying treatment. The temperature of the drying treatment is,for example, from 50° C. to 250° C., preferably from 60° C. to 150° C.,more preferably from 70° C. to 130° C. The time period of the dryingtreatment is, for example, from 0.1 minute to 30 minutes, preferablyfrom 0.2 minute to 10 minutes, more preferably from 0.3 minute to 3minutes. The temperature and time period of the drying treatment arepreferably lower and shorter in relation to, for example, continuousproductivity and the expression of a high porosity. When the conditionsare excessively severe, in, for example, the case where the liquid isapplied to the resin film, there is a risk in that the temperatureapproaches the glass transition temperature of the resin film toelongate the resin film in a drying furnace, and hence a defect such asa crack occurs in the formed pore structure immediately after theapplication. Meanwhile, when the conditions are excessively mild, theprecursor contains the residual solvent at, for example, the timing atwhich the precursor leaves the drying furnace, and hence aninconvenience in terms of appearance such as the occurrence of a scratchflaw may occur at the time of the rubbing of the precursor with a rollin the next step.

For example, the drying treatment may be natural drying, heat drying, ordrying under reduced pressure. Of those, heat drying is preferably usedwhen it is postulated that the optical member is continuously producedon an industrial scale. A method for the heat drying is not particularlylimited, and for example, general heating means may be used. Examples ofthe heating means include a hot-air heater, a heating roll, and a farinfrared heater. In addition, the solvent to be used is preferably asolvent having a low surface tension for the purpose of suppressing theoccurrence of a shrinkage stress along with the volatilization of thesolvent at the time of the drying and the crack phenomenon of the porelayer (silicone porous body) due to the occurrence. Examples of thesolvent include lower alcohols typified by isopropyl alcohol (IPA),hexane, and perfluorohexane. In addition, a small amount of aperfluoro-based surfactant or a silicone-based surfactant may be addedto IPA or the like described above to reduce its surface tension.

Further, as described above, the method of forming the low-refractiveindex layer includes the cross-linking reaction step of causing thecross-linking reaction in the precursor after the precursor-formingstep, and in the cross-linking reaction step, a basic substance isproduced by photoirradiation or heating. In addition, the cross-linkingreaction step is performed in a plurality of stages. At the first stageof the cross-linking reaction step, for example, the microporousparticles are chemically bonded to each other by the action of thecatalyst (basic substance). Thus, for example, the three-dimensionalstructure of each of the pulverized products in the coating film(precursor) is fixed. When conventional fixation based on sintering isperformed, the dehydration condensation of silanol groups in theprecursor and the formation of a siloxane bond are induced byperforming, for example, high-temperature treatment at 200° C. or more.In the formation method, when various additives that catalyze thedehydration condensation reaction are caused to react with the silanolgroups, the pore structure can be continuously formed and fixed at arelatively low drying temperature of around 100° C. and in a shorttreatment time of less than several minutes without occurrence of damageto, for example, the substrate (resin film).

A method for the chemical bonding is not particularly limited, and maybe appropriately determined in accordance with, for example, the kind ofthe gel-like silicon compound. As a specific example, the chemicalbonding may be performed by, for example, chemical cross-linking bondingbetween the pulverized products. In addition to the foregoing, forexample, when inorganic particles, each of which is made of, forexample, titanium oxide, and the like are added to the pulverizedproducts, it is conceivable that the inorganic particles and thepulverized products are chemically cross-linking bonded to each other.In addition, even when a biocatalyst such as an enzyme is carried on thesubstrate, a site of the catalyst different from its catalytic site andthe pulverized products may be chemically cross-linking bonded to eachother. Accordingly, the development of the application of the method offorming the low-refractive index layer not only to, for example, a porelayer (silicone porous body) formed of sol particles but also to anorganic-inorganic hybrid pore layer, a host-guest pore layer, and thelike is conceivable.

Which stage in the method of forming the low-refractive index layer thechemical reaction in the presence of the catalyst described above isperformed (occurs) at is not particularly limited, and the reaction isperformed at, for example, at least one stage in the above-mentionedmultistage cross-linking reaction step. For example, in the method offorming the low-refractive index layer, as described above, the dryingstep may also serve as the precursor-forming step. In addition, forexample, the following may be performed: the multistage cross-linkingreaction step is performed after the drying step; and the microporousparticles are chemically bonded to each other by the action of thecatalyst at least one stage of the step. For example, when the catalystis a photoactive catalyst as described above, in the cross-linkingreaction step, the microporous particles may be chemically bonded toeach other by photoirradiation to form the precursor of the porous body.In addition, when the catalyst is a thermally active catalyst, in thecross-linking reaction step, the microporous particles may be chemicallybonded to each other by heating to form the precursor of the porousbody.

The above-mentioned chemical reaction may be performed, for example, bysubjecting the coating film containing the catalyst added in advance tothe sol particle liquid (e.g., a suspension) to photoirradiation orheating, by blowing the catalyst onto the coating film and thensubjecting the coating film to the photoirradiation or the heating, orby subjecting the coating film to the photoirradiation or the heatingwhile blowing the catalyst onto the coating film. An integrated lightquantity in the photoirradiation is not particularly limited, and is,for example, from 200 mJ/cm² to 800 mJ/cm², preferably from 250 mJ/cm²to 600 mJ/cm², more preferably from 300 mJ/cm² to 400 mJ/cm² in terms ofa wavelength of 360 nm. An integrated light quantity of 200 mJ/cm² ormore is preferred from the viewpoint of preventing the following: anirradiation quantity is not sufficient, and hence the decomposition ofthe catalyst by its light absorption does not advance, with the resultthat its effect becomes insufficient. In addition, an integrated lightquantity of 800 mJ/cm² or less is preferred from the viewpoint ofpreventing the occurrence of a heat wrinkle due to the application ofdamage to the substrate below the pore layer. Conditions for the heatingtreatment are not particularly limited. A heating temperature is, forexample, from 50° C. to 250° C., preferably from 60° C. to 150° C., morepreferably from 70° C. to 130° C. A heating time is, for example, from0.1 minute to 30 minutes, preferably from 0.2 minute to 10 minutes, morepreferably from 0.3 minute to 3 minutes. Alternatively, the step ofdrying the sol particle liquid (e.g., a suspension) applied as describedabove may also serve as the step of performing the chemical reaction inthe presence of the catalyst. That is, in the step of drying the appliedsol particle liquid (e.g., a suspension), the pulverized products(microporous particles) may be chemically bonded to each other by thechemical reaction in the presence of the catalyst. In this case, thepulverized products (microporous particles) may be more strongly bondedto each other by further heating the coating film after the drying step.Further, it is assumed that the chemical reaction in the presence of thecatalyst occurs also in the step of producing the microporousparticle-containing liquid (e.g., a suspension) and the step of applyingthe microporous particle-containing liquid in some cases. However, theassumption does not limit the method of forming the low-refractive indexlayer. In addition, the solvent of the sol particle liquid to be used ispreferably a solvent having a low surface tension for the purpose of,for example, suppressing the occurrence of a shrinkage stress along withthe volatilization of the solvent at the time of its drying and thecrack phenomenon of the pore layer due to the occurrence. Examples ofthe solvent include lower alcohols typified by isopropyl alcohol (IPA),hexane, and perfluorohexane.

In the method of forming the low-refractive index layer, thecross-linking reaction step is performed in a plurality of stages, andhence the strength of the pore layer (low-refractive index layer) may befurther improved as compared to, for example, that in the case where thecross-linking reaction step is performed in one stage. The second andsubsequent steps of the cross-linking reaction step are hereinaftersometimes referred to as “aging step.” In the aging step, thecross-linking reaction may be further accelerated in the precursor by,for example, heating the precursor. Although a phenomenon occurring inthe cross-linking reaction step and a mechanism therefor are unclear,the phenomenon and the mechanism are, for example, as described above.In the aging step, both of a high porosity and high strength may beachieved, for example, as follows: while the shrinkage of the precursoris suppressed by setting a heating temperature to a low temperature, thecross-linking reaction is caused to improve the strength. Thetemperature in the aging step is, for example, from 40° C. to 70° C.,preferably from 45° C. to 65° C., more preferably from 50° C. to 60° C.The time period for which the aging step is performed is, for example,from 10 hr to 30 hr, preferably from 13 hr to 25 hr, more preferablyfrom 15 hr to 20 hr.

The low-refractive index layer formed as described above is excellent instrength, and hence may be turned into, for example, a roll-shapedporous body. Accordingly, the layer has such advantages as describedbelow: the production efficiency of the layer is satisfactory; and thelayer is easy to handle.

The low-refractive index layer (pore layer) formed as described abovemay be provided as, for example, a laminated structural body including aporous structure by being further laminated together with any other film(layer). In this case, the respective constituents in the laminatedstructural body may be laminated via, for example, a pressure-sensitiveadhesive or an adhesive. For example, the respective constituents may belaminated by continuous treatment including using an elongated film(e.g., a so-called roll-to-roll process) because the lamination can beefficiently performed. When the substrate is, for example, a moldedproduct or an element, the constituents subjected to batch treatment maybe laminated.

Details about specific configurations of the low-refractive index layerand the method of forming the low-refractive index layer are describedin, for example, WO 2019/151073 A1, the description of which isincorporated herein by reference.

B-4. First Pressure-Sensitive Adhesive Layer

The first pressure-sensitive adhesive layer has such hardness that undera normal state, a pressure-sensitive adhesive for forming the firstpressure-sensitive adhesive layer does not permeate the pores of thelow-refractive index layer. The storage modulus of elasticity of thefirst pressure-sensitive adhesive layer at 23° C. is from 1.0×10⁵ (Pa)to 1.0×10⁷ (Pa) as described above. The storage modulus of elasticityis, for example, 1.1×10⁵ (Pa) or more, 1.2×10⁵ (Pa) or more, 1.3×10⁵(Pa) or more, 1.4×10⁵ (Pa) or more, 1.5×10⁵ (Pa) or more, 1.6×10⁵ (Pa)or more, 1.7×10⁵ (Pa) or more, 1.8×10⁵ (Pa) or more, 1.9×10⁵ (Pa) ormore, or 2.0×10⁵ (Pa) or more, and 1.0×10⁷ (Pa) or less, 5.0×10⁵ (Pa) orless, 1.0×10⁶ (Pa) or less, or 5.0×10⁵ (Pa) or less. The storage modulusof elasticity is preferably from 1.3×10⁵ (Pa) to 1.0×10⁶ (Pa), morepreferably from 1.5×10⁵ (Pa) to 5.0×10⁵ (Pa). The storage modulus ofelasticity is determined by reading a value at 23° C. at the time ofmeasurement in conformity with a method described in JIS K 7244-1“Plastics-Determination of dynamic mechanical properties” under thecondition of a frequency of 1 Hz in the range of from −50° C. to 150° C.at a rate of temperature increase of 5° C./min.

Any appropriate pressure-sensitive adhesive may be used as thepressure-sensitive adhesive for forming the first pressure-sensitiveadhesive layer as long as the pressure-sensitive adhesive has suchcharacteristic as described above. The pressure-sensitive adhesive istypically, for example, an acrylic pressure-sensitive adhesive (acrylicpressure-sensitive adhesive composition). The acrylic pressure-sensitiveadhesive composition typically contains a (meth)acrylic polymer as amain component (base polymer). The (meth)acrylic polymer may beincorporated into the pressure-sensitive adhesive composition at a ratioof, for example, 50 wt % or more, preferably 70 wt % or more, morepreferably 90 wt % or more in the solid content of thepressure-sensitive adhesive composition. The (meth)acrylic polymercontains, as a main component, an alkyl (meth)acrylate serving as amonomer unit. The term “(meth)acrylate” refers to an acrylate and/or amethacrylate. The alkyl group of the alkyl (meth)acrylate is, forexample, a linear or branched alkyl group having 1 to 18 carbon atoms.The average number of carbon atoms of the alkyl group is preferably from3 to 9. As a monomer for forming the (meth)acrylic polymer, in additionto the alkyl (meth)acrylate, there are given comonomers, such as acarboxyl group-containing monomer, a hydroxyl group-containing monomer,an amide group-containing monomer, an aromatic ring-containing(meth)acrylate, and a heterocycle-containing (meth)acrylate. Thecomonomer is preferably a hydroxyl group-containing monomer and/or aheterocycle-containing (meth)acrylate, more preferablyN-acryloylmorpholine. The acrylic pressure-sensitive adhesivecomposition may preferably contain a silane coupling agent and/or across-linking agent. The silane coupling agent is, for example, an epoxygroup-containing silane coupling agent. The cross-linking agent is, forexample, an isocyanate-based cross-linking agent or a peroxide-basedcross-linking agent. Details about such pressure-sensitive adhesivelayer or acrylic pressure-sensitive adhesive composition are describedin, for example, JP 4140736 B2, the description of which is incorporatedherein by reference.

The thickness of the first pressure-sensitive adhesive layer ispreferably from 3 μm to 30 μm, more preferably from 5 μm to 10 μm. Whenthe thickness of the first pressure-sensitive adhesive layer fallswithin such ranges, the following advantage is obtained: an influence ofthe thickness of the pressure-sensitive adhesive layer on the entirethickness of the optical member is small while the layer has asufficient adhesive strength. Further, the above-mentioned desiredthickness ratio can be easily achieved.

B-5. Second Pressure-Sensitive Adhesive Layer

The second pressure-sensitive adhesive layer is applied to an apparatusthat may continuously vibrate at the time of its use, such as a vehicle,and the layer includes a pressure-sensitive adhesive having suchsoftness as to be capable of absorbing the transfer of the vibration tosuppress the breakage of the low-refractive index layer. The storagemodulus of elasticity of the second pressure-sensitive adhesive layer at23° C. is, for example, 1.0×10⁵ (Pa) or less as described above, and is,for example, 1.0×10⁵ (Pa) or less, 9.5×10⁴ (Pa) or less, 9.0×10⁴ (Pa) orless, 8.5×10⁴ (Pa) or less, 8.0×10⁴ (Pa) or less, 7.5×10⁴ (Pa) or less,or 7.0×10⁴ (Pa) or less, and 1.0×10³ (Pa) or more, 5.0×10³ (Pa) or more,1.0×10⁴ (Pa) or more, or 5.0×10⁴ (Pa) or more. The storage modulus ofelasticity is preferably from 5.0×10³ (Pa) to 9.0×10⁴ (Pa), morepreferably from 1.0×10⁴ (Pa) to 8.5×10⁴ (Pa).

Any appropriate pressure-sensitive adhesive may be used as thepressure-sensitive adhesive for forming the second pressure-sensitiveadhesive layer as long as the pressure-sensitive adhesive has suchcharacteristic as described above. The pressure-sensitive adhesive istypically, for example, an acrylic pressure-sensitive adhesive (acrylicpressure-sensitive adhesive composition). The acrylic pressure-sensitiveadhesive composition is as described in the section B-4. However, thepressure-sensitive adhesive for forming the second pressure-sensitiveadhesive layer is preferably free of a heterocycle-containing(meth)acrylate as a comonomer. In addition, the weight-average molecularweight Mw of a base polymer in the pressure-sensitive adhesivecomposition is preferably 2,000,000 or less, more preferably from 5,000to 1,600,000. Details about the second pressure-sensitive adhesive layeror the acrylic pressure-sensitive adhesive composition for forming thesecond pressure-sensitive adhesive layer are described in, for example,JP 2016-190996 A, the description of which is incorporated herein byreference.

The thickness of the second pressure-sensitive adhesive layer ispreferably from 5 μm to 300 μm, more preferably from 10 μm to 200 μm.When the thickness of the second pressure-sensitive adhesive layer fallswithin such ranges, impact is alleviated particularly at the time of thevibration of the optical member in a lateral direction, and hence damageto the low-refractive index layer can be reduced. In addition, strain ina configuration occurring at the time of the assembly of an imagedisplay apparatus is reduced, and as a result, brightness unevenness atthe time of image display can be reduced. Further, the above-mentioneddesired thickness ratio can be easily achieved.

C. Surface-Treated Layer

The dynamic friction coefficient of the surface-treated layer ispreferably 1.0 or less, more preferably 0.8 or less, still morepreferably 0.5 or less. The dynamic friction coefficient of thesurface-treated layer is preferably as small as possible, and the lowerlimit thereof may be, for example, 0.1. When the dynamic frictioncoefficient falls within such ranges, a reduction in display quality dueto wear or a flaw between the light guide plate and the reflectiveplate, and/or wear or a flaw between the light guide plate and a casingresulting from vibration at the time of the use of the optical membercan be suppressed. That is, when the surface-treated layer is arrangedas an outermost layer to make the optical member slippery, the wear orthe flaw (between the light guide plate and the reflective plate, and/orbetween the light guide plate and the casing) at the time of thevibration can be significantly suppressed. As a result, the reduction indisplay quality (substantially, display quality of the image displayapparatus) can be suppressed. Further, the breakage of thelow-refractive index layer due to the vibration can be suppressed by asynergistic effect of the arrangement of such surface-treated layer andthe setting of the storage modulus of elasticity of the secondpressure-sensitive adhesive layer described above within a predeterminedrange. The dynamic friction coefficient may be measured on the basis ofJIS K 7125 “Determination of the coefficients of friction.”

Any appropriate configuration may be adopted for the surface-treatedlayer as long as the layer can be formed on the surface of thereflective plate, and has such dynamic friction coefficient as describedabove. In one embodiment, the surface-treated layer may be a hard coatlayer. The hard coat layer has a pencil hardness of preferably H ormore, more preferably 2H or more, still more preferably 3H or more.Meanwhile, the pencil hardness of the hard coat layer is preferably 6Hor less, more preferably 5H or less. When the pencil hardness of thehard coat layer falls within such ranges, the breakage of thelow-refractive index layer can be suppressed while a reduction indisplay quality due to wear or a flaw resulting from the vibration ofthe optical member is suppressed. The pencil hardness may be measured onthe basis of JIS K 5400 “Pencil hardness test.”

The thickness of the hard coat layer is preferably from 1 μm to 30 μm,more preferably from 2 μm to 20 μm, still more preferably from 3 μm to15 μm. When the thickness of the hard coat layer falls within suchranges, the wear or the flaw can be more satisfactorily suppressed. Inaddition, the layer can be suppressed from causing interference fringeswhile having such hard pencil hardness as described above.

The hard coat layer may include any appropriate material as long as thelayer satisfies such characteristics as described above. The hard coatlayer is, for example, a cured layer of a thermosetting resin or a resincurable with an ionizing radiation (e.g., visible light or LUV light).Examples of such curable resin include: acrylates, such as urethane(meth)acrylate, polyester (meth)acrylate, and epoxy (meth)acrylate;silicon resins such as a siloxane; unsaturated polyester; and an epoxy.

Details about the hard coat layer are described in, for example, JP2011-237789 A, the description of which is incorporated herein byreference.

In one embodiment, the surface-treated layer may further include anoutermost layer containing fluorine on the surface of the hard coatlayer opposite to the reflective plate. The formation of such outermostlayer can further reduce the dynamic friction coefficient of thesurface-treated layer. The outermost layer may be formed by, forexample, applying a coating liquid containing a fluorine resin (e.g.,polytetrafluoroethylene), and drying, solidifying, or baking and curingthe liquid. The thickness of the outermost layer is preferably from 0.5μm to 20.0 μm.

D. Backlight Unit

The optical member described in the section A to the section C may besuitably used in a backlight unit (in particular, an edge light-typebacklight unit). Accordingly, the embodiment of the present inventionalso encompasses such backlight unit. The backlight unit includes theoptical member described in the section A to the section C and a lightsource. The light source may be, for example, a LED light source or anorganic EL light source. The light source is arranged so as to face theend surface 10 a of the light guide plate 10 of FIG. 1 .

E. Image Display Apparatus

The backlight unit of the section D may be suitably used in an imagedisplay apparatus (e.g., a liquid crystal display). Accordingly, theembodiment of the present invention also encompasses such image displayapparatus. The image display apparatus includes the backlight unitdescribed in the section D and an image display panel arranged on theemitting surface side of the light guide plate of the unit.

EXAMPLES

Now, the present invention is specifically described by way of Examples.However, the present invention is not limited to these Examples.Measurement methods for characteristics are as described below. Inaddition, unless otherwise specified, “%” and “part(s)” in Examples areby weight.

Production Example 1 Preparation of Coating Liquid for FormingLow-Refractive Index Layer (1) Gelation of Silicon Compound

0.95 g of methyltrimethoxysilane (MTMS) that was a precursor of asilicon compound was dissolved in 2.2 g of dimethyl sulfoxide (DMSO).Thus, a mixed liquid A was prepared. 0.5 g of a 0.01 mol/L aqueoussolution of oxalic acid was added to the mixed liquid A, and the mixturewas stirred at room temperature for 30 minutes so that MTMS washydrolyzed. Thus, a mixed liquid B containing tris(hydroxy)methylsilanewas produced.

0.38 g of 28 wt % ammonia water and 0.2 g of pure water were added to5.5 g of DMSO, and then the mixed liquid B was further added to themixture, followed by stirring at room temperature for 15 minutes toperform the gelation of tris(hydroxy)methylsilane.

Thus, a mixed liquid C containing a gel-like silicon compound wasobtained.

(2) Aging Treatment

Aging treatment was performed by incubating the mixed liquid Ccontaining the gel-like silicon compound, which had been prepared asdescribed above, as it was at 40° C. for 20 hours.

(3) Pulverization Treatment

Next, the gel-like silicon compound subjected to the aging treatment asdescribed above was crushed into granular shapes each having a size offrom several millimeters to several centimeters with a spatula. Next, 40g of isopropyl alcohol (IPA) was added to the mixed liquid C, and themixture was lightly stirred. After that, the mixture was left at rest atroom temperature for 6 hours so that the solvent and the catalyst in thegel were decanted. Similar decantation treatment was performed threetimes to replace the solvent with IPA. Thus, a mixed liquid D wasobtained. Next, the gel-like silicon compound in the mixed liquid D wassubjected to pulverization treatment (high-pressure media-lesspulverization). The pulverization treatment (high-pressure media-lesspulverization) was performed as follows: a homogenizer (manufactured bySMT Co., Ltd., product name: “UH-50”) was used, and 1.85 g of thegel-like silicon compound and 1.15 g of IPA in the mixed liquid D wereweighed in a 5-cubic centimeter screw bottle, followed by theperformance of the pulverization of the mixture under the conditions of50 W and 20 kHz for 2 minutes.

The gel-like silicon compound in the mixed liquid D was pulverized bythe pulverization treatment, and hence the mixed liquid was turned intoa sol liquid of the pulverized products (a mixed liquid D′). Avolume-average particle diameter representing a variation in particlesize of the pulverized products in the mixed liquid D′ was determined tobe from 0.50 to 0.70 with a dynamic light scattering-type nanotrackparticle size analyzer (manufactured by Nikkiso Co., Ltd., UPA-EX150).Further, a methyl ethyl ketone (MEK) solution of a photobase generator(Wako Pure Chemical Industries, Ltd.: product name: WPBG-266) having aconcentration of 1.5 wt % and a MEK solution of bis(trimethoxysilyl)ethane having a concentration of 5% were added at ratios of 0.062 g and0.036 g, respectively to 0.75 g of the sol liquid (mixed liquid D′).Thus, a coating liquid for forming a low-refractive index layer wasobtained.

Production Example 2 Preparation of Pressure-Sensitive Adhesive forForming First Pressure-Sensitive Adhesive Layer

90.7 Parts of butyl acrylate, 6 parts of N-acryloylmorpholine, 3 partsof acrylic acid, 0.3 part of 2-hydroxybutyl acrylate, and 0.1 part byweight of 2,2′-azobisisobutyronitrile serving as a polymerizationinitiator were loaded into a four-necked flask including a stirringblade, a temperature gauge, a nitrogen gas-introducing tube, and acondenser together with 100 g of ethyl acetate, and a nitrogen gas wasintroduced to purge the flask with nitrogen while the mixture was gentlystirred. After that, a liquid temperature in the flask was kept ataround 55° C., and a polymerization reaction was performed for 8 hoursto prepare an acrylic polymer solution. 0.2 Part of an isocyanatecross-linking agent (CORONATE L manufactured by Nippon PolyurethaneIndustry Co., Ltd., tolylene diisocyanate adduct of trimethylolpropane),0.3 part of benzoyl peroxide (NYPER BMT manufactured by Nippon Oil &Fats Co., Ltd.), and 0.2 part of γ-glycidoxypropylmethoxysilane(manufactured by Shin-Etsu Chemical Co., Ltd.: KBM-403) were blendedinto 100 parts of the solid content of the resultant acrylic polymersolution to prepare an acrylic pressure-sensitive adhesive solution.Next, the acrylic pressure-sensitive adhesive solution was applied toone surface of a silicone-treated polyethylene terephthalate (PET) film(manufactured by Mitsubishi Chemical Polyester Film Co., Ltd.,thickness: 38 μm) so that the thickness of a pressure-sensitive adhesivelayer after drying became 20 μm, followed by drying at 150° C. for 3minutes. Thus, the pressure-sensitive adhesive layer was formed. Theresultant pressure-sensitive adhesive layer had a storage modulus ofelasticity of 1.3×10⁵ (Pa).

Production Example 3 Preparation of Pressure-Sensitive Adhesive forForming Second Pressure-Sensitive Adhesive Layer

99 Parts of butyl acrylate, 1 part of 4-hydroxybutyl acrylate, and 0.1part of 2,2′-azobisisobutyronitrile serving as a polymerizationinitiator were loaded into a four-necked flask including a stirringblade, a temperature gauge, a nitrogen gas-introducing tube, and acondenser together with 100 parts of ethyl acetate, and a nitrogen gaswas introduced to purge the flask with nitrogen while the mixture wasgently stirred. After that, a liquid temperature in the flask was keptat around 55° C., and a polymerization reaction was performed for 8hours to prepare an acrylic polymer solution. 0.1 Part of an isocyanatecross-linking agent (TAKENATE D110N manufactured by Mitsui TakedaChemicals Inc., trimethylolpropane xylylene diisocyanate), 0.1 part ofbenzoyl peroxide (NYPER BMT manufactured by Nippon Oil & Fats Co.,Ltd.), and 0.2 part of γ-glycidoxypropylmethoxysilane (manufactured byShin-Etsu Chemical Co., Ltd.: KBM-403) were blended into 100 parts ofthe solid content of the resultant acrylic polymer solution to preparean acrylic pressure-sensitive adhesive composition solution. Next, theacrylic pressure-sensitive adhesive composition solution was applied toone surface of a polyethylene terephthalate film treated with asilicone-based releasing agent (separator film: manufactured byMitsubishi Chemical Polyester Film Co., Ltd., MRF 38), and was dried at150° C. for 3 minutes to form a pressure-sensitive adhesive layer havinga thickness of 20 μm on the surface of the separator film. The resultantpressure-sensitive adhesive layer had a storage modulus of elasticity of8.2×10⁴ (Pa).

Production Example 4 Production of Double-Sided Pressure-SensitiveAdhesive Film

The coating liquid for forming a low-refractive index layer prepared inProduction Example 1 was applied to a substrate having a thickness of 20μm (acrylic film). The wet thickness (thickness before drying) of thecoating layer was about 27 μm. The coating layer was treated at atemperature of 100° C. for 1 minute to be dried. Thus, a low-refractiveindex layer (thickness: 0.9 μm) was formed on the substrate. Theresultant low-refractive index layer had a porosity of 56% and arefractive index of 1.15. Next, a first pressure-sensitive adhesivelayer (thickness: 10 μm) including the pressure-sensitive adhesiveprepared in Production Example 2 was formed on the surface of thelow-refractive index layer. Further, a second pressure-sensitiveadhesive layer (thickness: 28 μm) including the pressure-sensitiveadhesive prepared in Production Example 3 was formed on the surface ofthe substrate. Thus, a double-sided pressure-sensitive adhesive film,which had the configuration “first pressure-sensitive adhesive layer(high storage modulus of elasticity)/low-refractive indexlayer/substrate/second pressure-sensitive adhesive layer (low storagemodulus of elasticity),” was produced. The ratio of the thickness of thelow-refractive index layer to the total thickness of thepressure-sensitive adhesive layers was 1.5%. The refractive index of thelow-refractive index layer was measured as described below.

After the low-refractive index layer had been formed on the acrylicfilm, the resultant was cut into a size measuring 50 mm by 50 mm, andthe piece was bonded to the front surface of a glass plate (thickness: 3mm) via a pressure-sensitive adhesive layer. A central portion (having adiameter of about 20 mm) on the rear surface of the glass plate wasdaubed with a black marker pen. Thus, a sample in which light was notreflected on the rear surface of the glass plate was obtained. Thesample was set in an ellipsometer (manufactured by J. A. Woollam Japan:VASE), and its refractive index was measured under the conditions of awavelength of 550 nm and an incident angle of from 50° to 80°.

Production Example 5 Preparation of Hard Coat Layer-Forming Material

To a resin solution (manufactured by DIC Corporation, product name:“UNIDIC 17-806”, solid content concentration: 80%) obtained bydissolving, in butyl acetate, a UV-curable resin monomer or oligomercontaining urethane acrylate as a main component, 5 parts of aphotopolymerization initiator (manufactured by BASF SE, product name:“IRGACURE 906”) and 0.03 part of a leveling agent (manufactured by DICCorporation, product name: “GRANDIC PC4100”) per 100 parts of the solidcontent in the solution were added. After that, butyl acetate was addedto the solution so that the solid content concentration in the solutionbecame 75%. Further, cyclopentanone was added to the solution so thatthe solid content concentration in the solution became 50%. Thus, a hardcoat layer-forming material for forming a hard coat layer was prepared.

Example 1

The hard coat layer-forming material obtained in Production Example 5was applied to one surface of a reflective plate (manufactured by TorayIndustries, Inc., product name: “LUMIRROR (trademark) #225 E6SR”) with adie coater to form a coating film. The hard coat layer-forming materialwas applied in a thickness of 13.8 μm so that the thickness of thecoating film after its curing (hard coat layer) became 7.5 μm. Thecoating film was dried at 80° C. for 2 minutes, and then the coatingfilm was irradiated with UV light having an integrated light quantity of300 mJ/cm² through use of a high-pressure mercury lamp. Thus, a hardcoat layer was formed. The hard coat layer had a dynamic frictioncoefficient of 0.8 and a pencil hardness of 2H. The surface of thereflective plate on which the hard coat layer was not formed and thedouble-sided pressure-sensitive adhesive film obtained in ProductionExample 4 were bonded to each other via the second pressure-sensitiveadhesive layer. Further, a commercial light guide plate was bonded tothe resultant via the first pressure-sensitive adhesive layer. Thus, anoptical member was produced. The dynamic friction coefficient wasmeasured on the basis of JIS K 7125 “Determination of the coefficientsof friction,” and the pencil hardness was measured on the basis of JIS K5400 “Pencil hardness test.”

(I) Flaw Test

The laminate of the double-sided pressure-sensitive adhesive film andthe reflective plate used in the optical member was subjected to a flawtest. A specific procedure is as described below. The laminate was cutinto a size measuring 50 mm by 1,500 mm, and was bonded to a glass platevia the first pressure-sensitive adhesive layer to produce a testsample. Next, the test sample and a diffusing sheet (manufactured bySumitomo 3M Limited, product name: “DBEF-D2-400”) were arranged in atray so that the reflective plate (substantially, the hard coat layer)of the sample and the sheet were brought into contact with each other,followed by a vibration test at 200 times/min for 10 minutes. A flaw inthe reflective plate after the vibration test was visually observed, andwas evaluated by the following criteria. The result is shown in Table 1.

Satisfactory: No flaw was observed on the surface of the reflectiveplate.

Unsatisfactory: A flaw was observed on the surface of the reflectiveplate.

(II) Reworkability

The resultant optical member was arranged in the back surface-sidecasing of a liquid crystal display apparatus, and was then removed. Themember was arranged in the back surface-side casing again, and wasevaluated by the following criteria. The result is shown in Table 1.

Satisfactory: The member was able to be rearranged.

Unsatisfactory: The member could not be rearranged (the laminate broke).

Example 2

An optical member was produced in the same manner as in Example 1 exceptthat a fluorine coating layer was formed as an outermost layercontaining fluorine on the surface of the hard coat layer. The fluorinecoating layer was formed by using a commercial fluorine resin coatingspray (manufactured by Taihei Kasei Co., Ltd., product name: “JETPROTECTOR F-200SI”). The fluorine coating layer had a thickness of 15 μmand a dynamic friction coefficient of 0.4. The resultant optical memberwas subjected to the same evaluations as those of Example 1. The resultsare shown in Table 1.

Comparative Example 1

An optical member was produced in the same manner as in Example 1 exceptthat no hard coat layer was formed. The surface of the reflective platehad a dynamic friction coefficient of 1.1. The resultant optical memberwas subjected to the same evaluations as those of Example 1. The resultsare shown in Table 1.

Comparative Example 2

The surface of the reflective plate of the optical member of ComparativeExample 1 was bonded to the back surface-side casing of a liquid crystaldisplay apparatus with a commercial double-sided tape, and was thenpeeled. The surface was arranged in (bonded to) the back surface-sidecasing again, and was evaluated by the same criteria as those ofExample 1. The result is shown in Table 1.

TABLE 1 Dynamic friction coefficient Flaw test Reworkability Example 10.8 Satisfactory Satisfactory Example 2 0.4 Satisfactory SatisfactoryComparative 1.1 Unsatisfactory Satisfactory Example 1 Comparative — —Unsatisfactory Example 2

As is apparent from Table 1, according to Examples of the presentinvention, an optical member suppressed from causing a flaw due tovibration can be achieved. It is understood that such optical member issuppressed from causing a reduction in display quality due to a flaw orwear. Further, it is found that according to Examples of the presentinvention, the low-refractive index layer is not broken even by thevibration.

INDUSTRIAL APPLICABILITY

The optical member of the present invention may be suitably used in thebacklight unit of an image display apparatus (in particular, a liquidcrystal display apparatus). The image display apparatus may be suitablyused in on-vehicle applications and/or amusement applications.

REFERENCE SIGNS LIST

-   10 light guide plate-   20 double-sided pressure-sensitive adhesive film-   21 first pressure-sensitive adhesive layer-   22 low-refractive index layer-   23 second pressure-sensitive adhesive layer-   24 substrate-   30 reflective plate-   40 surface-treated layer-   100 optical member

1. An optical member, comprising: a light guide plate having an endsurface that light from a light source enters and an emitting surfacefrom which the entered light is emitted; and a reflective plate bondedto a side of the light guide plate opposite to the emitting surface viaa double-sided pressure-sensitive adhesive film, wherein thedouble-sided pressure-sensitive adhesive film includes a firstpressure-sensitive adhesive layer, a low-refractive index layer, and asecond pressure-sensitive adhesive layer from a light guide plate side,and wherein the optical member further comprises a surface-treated layerformed on a side of the reflective plate opposite to the double-sidedpressure-sensitive adhesive film.
 2. The optical member according toclaim 1, wherein the surface-treated layer has a dynamic frictioncoefficient of 1.0 or less.
 3. The optical member according to claim 1,wherein the surface-treated layer is a hard coat layer having a pencilhardness of H or more.
 4. The optical member according to claim 3,wherein the surface-treated layer further includes an outermost layercontaining fluorine on a surface of the hard coat layer opposite to thereflective plate.
 5. A backlight unit, comprising: the optical member ofclaim 1; and a light source, wherein the light source is arranged so asto face the end surface of the light guide plate.
 6. An image displayapparatus, comprising: the backlight unit of claim 5; and an imagedisplay panel arranged on an emitting surface side of the light guideplate.
 7. The backlight unit according to claim 1, wherein thelow-refractive index layer has pores therein and the porosity of thelow-refractive index layer is 40% or more and 85% or less.
 8. Thebacklight unit according to claim 1, wherein a size of each of the poresin the low-refractive index layer is from 2 nm to 500 nm.
 9. Thebacklight unit according to claim 1, wherein the low-refractive indexlayer has a refractive index of 1.30 or less.
 10. The backlight unitaccording to claim 1, wherein the low-refractive index layer has a hazeof less than 5%.
 11. The backlight unit according to claim 1, whereinthe low-refractive index layer has a thickness of from 0.2 μm to 5 μm.12. The backlight unit according to claim 1, wherein the low-refractiveindex layer is formed of one or a plurality of kinds of constituentunits each forming a fine pore structure, and the constituent units arechemically bonded to each other through a catalytic action.
 13. Thebacklight unit according to claim 1, wherein the firstpressure-sensitive adhesive layer is adjacent to the low-refractiveindex layer and has a storage modulus of elasticity of from 1.3×10⁵ (Pa)to 1.0×10⁶ (Pa).
 14. The backlight unit according to claim 1, whereinthe second pressure-sensitive adhesive layer has a storage modulus ofelasticity of from 5.0×10³ (Pa) to 9.0×10⁴ (Pa).
 15. An optical member,comprising: a light guide plate having an end surface that light from alight source enters and an emitting surface from which the entered lightis emitted; and a reflective plate bonded to a side of the light guideplate opposite to the emitting surface via a double-sidedpressure-sensitive adhesive film, wherein the double-sidedpressure-sensitive adhesive film includes a first pressure-sensitiveadhesive layer, a low-refractive index layer, and a secondpressure-sensitive adhesive layer from a light guide plate side, whereinthe optical member further comprises a surface-treated layer formed on aside of the reflective plate opposite to the double-sidedpressure-sensitive adhesive film, wherein the surface-treated layer hasa dynamic friction coefficient of 1.0 or less, wherein thelow-refractive index layer is formed of one or a plurality of kinds ofconstituent units each forming a fine pore structure, and theconstituent units are chemically bonded to each other through acatalytic action, wherein the low-refractive index layer has porestherein and the porosity of the low-refractive index layer is 40% ormore and 85% or less, wherein a size of each of the pores in thelow-refractive index layer is from 2 run to 500 nm, wherein thelow-refractive index layer has a refractive index of 1.30 or less, has ahaze of less than 5%, and has a thickness of from 0.2 μm to 5 μm,wherein the first pressure-sensitive adhesive layer is adjacent to thelow-refractive index layer and has a storage modulus of elasticity offrom 1.3×10⁵ (Pa) to 1.0×10⁶ (Pa), and wherein the secondpressure-sensitive adhesive layer has a storage modulus of elasticity offrom 5.0×10³ (Pa) to 9.0×10⁴ (Pa).